The most common cause of a gallbladder infection is a gallstone getting stuck in the narrow duct that drains bile out of the gallbladder. When bile can’t flow out, it builds up, the gallbladder wall swells, and bacteria that normally pass through harmlessly begin to multiply in the stagnant fluid. This condition, called cholecystitis, can also develop without gallstones in people who are critically ill or have certain chronic diseases.
How Gallstones Trigger Infection
Your gallbladder stores bile, a digestive fluid made by the liver. After you eat, the gallbladder squeezes bile through a small tube called the cystic duct and into the intestine. A gallstone can become wedged in that duct like a cork in a bottle. Once the duct is blocked, bile has nowhere to go.
Trapped bile irritates and inflames the gallbladder wall. The tissue swells, pressure builds, and blood flow to the wall can slow down. This creates ideal conditions for bacteria already present in bile to flourish. Bacterial growth in bile occurs in roughly 20% to 70% of patients with acute cholecystitis, depending on how severe the episode is. The bacteria most commonly involved are gut organisms like E. coli and Klebsiella, along with streptococci and other species that thrive in low-oxygen environments. In more severe cases, a wider variety of bacterial species tends to show up.
Not every blocked duct leads to full-blown infection. Sometimes the stone shifts on its own and bile flow resumes before bacteria take hold. But the longer the blockage lasts, the higher the risk of serious inflammation and bacterial infection developing together.
Causes That Don’t Involve Gallstones
About 5% to 10% of gallbladder infections happen without any stones at all. This form, called acalculous cholecystitis, develops when the gallbladder stops contracting normally and bile becomes thick and stagnant. Two main situations lead to this.
The first is critical illness. People in intensive care units, on mechanical ventilation, recovering from major surgery, or dealing with severe burns, trauma, or sepsis are at elevated risk. In these patients, fever and dehydration thicken the bile. At the same time, because they aren’t eating by mouth, the hormonal signal that normally triggers gallbladder contractions never fires. The combination of thick bile and a motionless gallbladder leads to stasis, inflammation, and sometimes reduced blood flow to the gallbladder wall itself.
The second group includes people with chronic conditions who aren’t necessarily hospitalized. Diabetes, heart failure, high blood pressure, and end-stage kidney disease all increase the risk. Patients receiving nutrition entirely through an IV (total parenteral nutrition) for more than three months are also vulnerable, again because the gallbladder rarely gets the signal to squeeze. Acalculous cholecystitis has also been reported during pregnancy, as a complication of hepatitis A, and in people with advanced HIV infection.
Other Blockages Beyond Stones
Gallstones aren’t the only thing that can plug the drainage system. Biliary sludge, a thick mixture of tiny cholesterol crystals and other particles, can accumulate and obstruct the duct in much the same way a stone does. Sludge often forms during periods of fasting, rapid weight loss, or pregnancy, and it sometimes precedes the development of actual gallstones.
Tumors in or near the bile ducts can also block flow. Less commonly, kinking or scarring of the bile ducts from previous inflammation or surgery creates a mechanical obstruction that traps bile and sets the stage for infection.
Who Is Most at Risk
Gallbladder infections follow the risk profile of gallstones themselves, since stones are the dominant cause. Women are affected more often than men, accounting for roughly 60% to 65% of cases in most studies. The hormone estrogen raises cholesterol levels in bile, which promotes stone formation. Pregnancy, hormonal birth control, and hormone replacement therapy all amplify this effect.
Age is another strong predictor. People over 35 make up the large majority of cases, and risk continues to climb with each decade. Carrying extra body weight also matters: obesity changes bile composition in ways that favor crystal and stone formation, and about a third of cholecystitis patients in epidemiological studies are obese.
Rapid weight loss deserves special mention. Losing weight quickly, whether through very low-calorie diets or bariatric surgery, causes the liver to dump extra cholesterol into bile. At the same time, the gallbladder may contract less frequently because food intake is reduced. This one-two punch makes new stone formation surprisingly common during aggressive dieting.
What Happens Inside the Gallbladder
Once inflammation takes hold, the process can escalate in stages. Early on, the gallbladder wall becomes swollen and red, and fluid may collect around the outside of the organ. Doctors can see this fluid on ultrasound, which is one of the key imaging signs used to confirm the diagnosis alongside tenderness in the upper right abdomen, fever, and elevated markers of inflammation in blood tests.
If the infection continues unchecked, pressure inside the gallbladder keeps rising. The wall can develop patches where blood flow is cut off, leading to tissue death (gangrene). In the worst cases, the weakened wall tears open, spilling infected bile into the abdominal cavity and causing peritonitis, a dangerous widespread infection. An abscess, a walled-off pocket of pus, can also form around the gallbladder.
These complications are the reason gallbladder infections are treated urgently. Most patients are started on antibiotics and scheduled for surgical removal of the gallbladder, typically through small incisions using a camera-guided approach. The surgery is straightforward when performed early but becomes more complex once the tissue is severely inflamed or damaged.
Symptoms That Point to a Gallbladder Infection
The hallmark symptom is steady, intense pain in the upper right side of your abdomen that lasts longer than a few hours. This distinguishes it from a typical gallstone attack, which usually peaks and fades within one to three hours. With cholecystitis, the pain doesn’t let up, and it often worsens when you breathe deeply or press on the area.
Fever is common, though not always high. Nausea and vomiting frequently accompany the pain. Some people notice the pain spreading to their right shoulder or back. If the infection becomes severe, signs like a racing heartbeat, confusion, or a rigid abdomen suggest complications that need immediate attention.
Pain that follows a fatty meal and resolves on its own is more likely a gallstone episode without infection. Pain that persists beyond six hours, especially with fever, is the pattern that raises concern for true cholecystitis.